This invention relates to a combinatorial weighing method and apparatus in an automatic weighing system of the combinatorial type. More particularly, the invention relates to a combinatorial weighing method and apparatus for measuring the weight of a batch of articles introduced into each of a plurality of weighing machines, forming the weight values provided by the weighing machines into combinations, selecting the combination of weighing machines whose articles have a total combined weight within a preset allowable range, and discharging the articles from the selected combination of weighing machines.
According to a combinatorial weighing apparatus which is known in the art, combinatorial weighing is carried out by weighing batches of articles which have been introduced into a plurality of weighing machines, forming combinations of the weight values from the weighing machines, obtaining a combination (referred to as the "optimum combination") the total weight of which is equal to a preset weight value or closest to the preset weight value within preset allowable limits, discharging the articles from the machines belonging to the combination obtained, subsequently replenishing the weighing machines, which have discharged their articles, with articles in order to prepare for the next combination, and continuing automatic weighing by repeating the foregoing operations.
In a combinatorial weighing apparatus of the foregoing type, a combinatorial weighing technique customarily employed is referred to as a so-called "minus-cut method" wherein the lower limit value of the preset allowable limits is so determined as to be equal to the preset weight value. The reason is that setting the lower limit value to one below the preset weight value can have the undesirable result of providing a batch of discharged articles the total weight of which is too low. With the minus-cut method, a mean weight value W.sub.m obtained over a plurality of weighing cycles always falls within a range between a preset weight value W.sub.s and an upper limit weight value W.sub.max, as shown in FIG. 1. Therefore, as a result of adopting the minus-cut method, the total weight of the combination obtained in every weighing cycle must be made greater than the preset weight value. This is a disadvantage in that it results in a lower yield on the producer's, or seller's, side.
Accordingly, in some countries it is legally permitted to adopt a lower limit value W.sub.min, namely the lower limit of the aforementioned preset allowable limits, which is below the preset value W.sub.s. In other words, if the total weight of a combination resides within the limits of a predetermined precentage (e.g., 4.5%) about a central value which is the preset weight value, then shipment of the product is allowed even if the total weight of the combination is below the preset weight value. For consumer protection, however, the producer is obligated to adopt a mean weight value W.sub.m for shipment which is greater than the preset weight value W.sub.s, as shown in FIG. 2.